It is already known to internally reform the domed base of a beverage can to provide a re-entrant profile. This technique is primarily used to increase the strength of the base, which in turn allows light weighting. For example, EP 0482581 A (BALL CORP) 29.02.1992 describes an apparatus suitable for reforming the base of a beverage can in this way. In particular, FIG. 11 of this application shows an enlarged cross-section view through a portion of the base of a beverage can after such reforming.
WO 96/24539 (KOHORN INTERNATIONAL PTY LIMIT) 15.08.1996 describes a container formed with an open void separate from the main containment volume. Examples of such containers are metal cans, which are formed with a generally concave or domed void in the base, as commonly used for soft drinks, beer etc. This document describes removal means that are provided to substantially close this void, thereby creating a second containment volume that may be used for promotional goods, a second active ingredient or such like.
Both these ideas are combined in EP 0958182 B (SCHMALBACH LUBECA) 24.11.1999 which describes a two piece beverage can made substantially of sheet metal having a base that is drawn-in to the inner side of the container, so that the diameter of the base is evidently smaller than the diameter of the container. This document also describes a separate disc-shaped component that is adapted to be fixed into the base. The separate disc-shaped component (“false bottom part”) is separately produced and may therefore be easily decorated etc.